The present invention relates to novel pipe joints, and more particularly, it relates to autogenous welding of large diameter pipes and to the piping so produced.
The pipes or tubes contemplated according to the present invention are typified by pipelines having a 200 mm or greater diameter. These pipes are presently prepared in lengths of six to 15 meters and are provided with anti-corrosion interior coatings or anti-abrasion coatings, depending upon the fluid to be carried. As contemplated herein, fluids is used in the most general sense to include petroleum liquids, water, chemical and alkaline solutions, aqueous suspensions of solids, such as coal particles, slurries, and the like.
Pipes used to transport such fluids are usually provided with interior protection which can be, according to the use and degree of evolution of the technique, of centrifugal cement, bitumens, polyurethane coatings, and cold-hardened catalyzed epoxy resin coatings.
With all such coatings, because of, respectively, their tendency to crack, their fusibility, and their tendency to pyrolyze at the welding temperature for the pipes, there has been a need to keep at the ends of the pipes an uncoated band which can vary from about one-half to about two pipe diameters depending on the pipe size, the wall thickness of the pipe, and the type of coating.
These uncoated portions are then the site of heavy local corrosion, requiring the costly replacement of the piping over greater or lesser periods of time.
Some of the solutions call for metal flanges faced with elastomeric material which rest on the interior coating, which is utilized in such cases without an uncoated zone at the ends of the pipe sections. The drawback of such solution is that they do not resist high pressure and can be used only at lower pressures below 35 bars.
Another solution involves utilizing stainless steel connecting sleeves. It is a solution which is always costly and can at the same time lead to complications when the interior coating of the tube is thick where a special abrasion resistance is sought.
Methods have been described in certain prior art patents. U.K. Patent No. 401,615 shows a double conical ring fitted with a positioning rib, which centers the ends of the pipes to be joined. French Pat. No. 992,388 inserts a grooved ring with clearance into each end of the pipe. The exterior edge of the ring forms a ridge to permit welding to the end of the pipe. Thus, a shoulder piece according to the coating thickness must be contemplated, and a tight joint is, in such case, critical.